Transcript structure of nephron functions of kidney

DEPARTMENT OF PHSIOLOGY
DR.TAYYABA AZHAR
 1:
Excretion of metabolic waste products and
foreign chemicals
 2: Regulation of water and electrolyte balances
 3: Regulation of body fluid osmolality and
electrolyte concentrations
 4: Regulation of arterial pressure
 5: Regulation of acid-base balance
 6: Secretion, metabolism, and excretion of
hormones
 7: Gluconeogenesis
1) Urea (from the metabolism of amino acids)
2) Creatinine (from muscle creatine)
3) Uric acid (from nucleic acids)
4) Hemoglobin breakdown (such as bilirubin)
5) Metabolites of various hormones.
6) The kidneys also eliminate toxins , foreign
substances that are either produced by the body or
ingested, such as pesticides, drugs, and food
additives.
 For
maintenance of homeostasis, excretion
of water and electrolytes must precisely
match intake. If intake exceeds excretion,
the amount of that substance in the body
will increase. If intake is less than excretion,
the amount of that substance in the body
will decrease.
 The
kidneys contribute to acid-base regulation,
along with the lungs and body fluid buffers, by
excreting acids and by regulating the body fluid
buffer stores. The kidneys are the only means of
eliminating from the body certain types of acids,
such as sulfuric acid and phosphoric acid,
generated by the metabolism of proteins.
 The
kidneys secrete erythropoietin, which
stimulates the production of red blood cells One
important stimulus for erythropoietin secretion by
the kidneys is hypoxia. The kidneys normally
account for almost all the erythropoietin secreted
into the circulation.
The kidneys produce the active form of vitamin
D, 1,25-dihydroxyvitamin D3 (calcitriol), by
hydroxylating this vitamin at the “number 1”
position.
 Calcitriol
is essential for normal calcium
deposition in bone and calcium reabsorption by the
gastrointestinal tract.

 The
kidney’s synthesize glucose from amino
acids and precursors during prolonged
fasting,
a
process
referred
to
as
gluconeogenesis.
 The kidney’s capacity to add glucose to the
blood during prolonged periods of fasting
rivals that of the liver.
 The
two kidneys lie on the posterior wall of the
abdomen, outside the peritoneal cavity.
 Each kidney of the adult human weighs about 150
grams and is size of a clenched fist.
 The medial side of each kidney contains hilum
through which pass the renal artery and vein,
lymphatics, nerve supply, and ureter, which carries
the final urine from the kidney to the bladder,
where it is stored until emptied.
 If
the kidney is bisected from top to bottom, the
two major regions that can be visualized are the
outer cortex and the inner region medulla.
 The medulla is divided into multiple cone-shaped
masses of tissue called renal pyramids.
 The base of each pyramid originates at the border
between the cortex and medulla and terminates in
the papilla, which projects into the space of the
renal pelvis, a funnel-shaped continuation of the
upper end of the ureter.
 Nephron
is the functional unit of kidney.
 Each kidney in the human contains about 1 million
nephrons, each capable of forming urine.
 The kidney cannot regenerate new nephrons.
Therefore,with renal injury, disease, or normal
aging, there is a gradual decrease in nephron
number.
 After age 40, the number of functioning nephrons
usually decreases about 10 per cent every 10 years;
thus, at age 80, many people have 40 per cent
fewer functioning nephrons than they did at age
40.
 Each
nephron contains :
 (1) A tuft of glomerular capillaries called the
glomerulus, through which large amounts of fluid
are filtered from the blood.
 (2) A long tubule in which the filtered fluid is
converted into urine on its way to the pelvis of the
kidney.
 The
glomerulus contains a network of branching
and anastomosing glomerular capillaries that,
compared with other capillaries, have high
hydrostatic pressure (about 60 mm Hg).

The glomerular capillaries are covered by
epithelial cells, and total glomerulus is encased in
Bowman’s capsule. Fluid
filtered from the
glomerular capillaries flows into Bowman’s
capsule and then into the proximal tubule, which
lies in the cortex of the kidney.
 The
glomerulus- (a ball of capillaries) filters H2O and
solute from blood
 Afferent arterioles (come from renal artery)- one supplies
each nephron and delivers blood to glomerulus
 Efferent arterioles (come from glomerular capillaries)unfiltered blood leaves glomerulus
 Peritubular capillaries- supply renal tissue with blood.
 Bowman’s
capsule- collects glomerular filtrate
 Proximal tubule- uncontrolled reabsorption and
secretion of selected substances
 Loop of Henle – establishes an osmotic gradient in
order to concentrate urine to appropriate amount
 Distal tubule- controlled reabsorption and secretion
occur here
 collecting duct (tubule)- variable, controlled
reabsorption of Na+ and H2O, and secretion of K+ and
H+ (fluid leaving here is urine-enters renal pelvis)
 The
ascending limb of Henle passes through a fork
formed by the afferent and efferent arterioles of the
same nephron.
 The vascular and tubular cells at this juncture are
both specialized to form the JGA.
Proximal tubule
Juxtaglomerular
apparatus
Distal
tubule
Collecting
duct
Efferent
arteriole
Afferent
arteriole
Bowman’s
capsule
Glomerulus
Artery
Vein
Cortex
Medulla
Peritubular
capillaries
Overview of Functions of Parts of a Nephron
Loop of
Henle
To renal
pelvis
Fig. 14-3, p. 504
Proximal
tubule
Distal
tubule
Distal
tubule
Glomerulus
Bowman’s
capsule
Proximal
tubule
Cortex
Medulla
Collecting
duct
Descending
limb of
loop of
Henle
Loop of Henle
Other nephrons emptying into
the same collecting duct
Vasa recta
Ascending
limb of
loop of
Henle
To renal
pelvis
Fig. 14-5, p. 505
flow to the two kidneys is 22 % of the
cardiac output, or 1100 ml/min.
 The renal artery enters the kidney through the
hilum and then branches progressively to form the
 A) Interlobar arteries,
 B)Arcuate arteries,
 C) Interlobular arteries (also called radial arteries)
 and afferent arterioles which lead to the
glomerular capillaries, where large amounts of
fluid and solutes (except the plasma proteins) are
filtered to begin urine formation.
 Blood
 The
distal ends of the capillaries of each
glomerulus coalesce to form the efferent arteriole,
which leads to a second capillary network.
 The peritubular capillaries, that surrounds the
renal tubules.
 The
renal circulation is unique in that it has two
capillary beds, the glomerular and peritubular
capillaries,which are arranged in series and
separated by the efferent arterioles, which help
regulate the hydrostatic pressure in both sets of
capillaries.
High hydrostatic pressure in the glomerular
capillaries (about 60 mm Hg) causes rapid fluid
filtration.
 Where as a much lower hydrostatic pressure in the
peritubular capillaries (about 13 mm Hg) permits
rapid fluid reabsorption.

CORTICAL NEPHRON
Nephron glomeruli
located in outer
cortex is called
cortical nephron.
 Short loops of henle.
 Blood supply by
peritubular
capillaries.

MEDULLARY NEPHRON
Nephron glomeruli located in
medulla called
juxtamedullary nephron.
 Long loop of henle dip deeply
into medulla.
 Specialized peritubular
capillaries vasa recta which
forms hair pin loops.
 Specialized network of
capillaries have role in
formation of concentrated
urine.